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Correct blur radius after Box-Muller

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This commit is contained in:
Steven Robertson
2011-10-27 10:36:44 -04:00
parent 1faffa1d14
commit 77daf5e639
1 changed files with 5 additions and 2 deletions
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7
cuburn/code/variations.py
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@ -332,7 +332,10 @@ var(34, 'blur', """
var(35, 'gaussian_blur', """
float ang = mwc_next_01(rctx) * 2.0f * M_PI;
float r = w * sqrtf(-2.0f * log2f(mwc_next_01(rctx)) / M_LOG2E);
// constant factor here is stdev correction for converting to Box-Muller;
// np.std(np.sum(np.random.random((1<<30, 4)), axis=1) - 2)
// TODO: maybe derive it analytically
float r = w * 0.57736 * sqrtf(-2.0f * log2f(mwc_next_01(rctx)) / M_LOG2E);
ox += r * cosf(ang);
oy += r * sinf(ang);
""")
@ -342,7 +345,7 @@ var(36, 'radial_blur', """
float spinvar = sinf(blur_angle);
float zoomvar = cosf(blur_angle);
float r = w * sqrtf(-2.0f * log2f(mwc_next_01(rctx)) / M_LOG2E);
float r = w * 0.57736 * sqrtf(-2.0f * log2f(mwc_next_01(rctx)) / M_LOG2E);
float ra = sqrtf(tx*tx + ty*ty);
float tmpa = atan2f(ty, tx) + spinvar * r;
float rz = zoomvar * r - 1.0f;